Yes, to cool the reactor core and any onsite spent fuel pool. Here is an informed comment by reader “EL” on BraveNewClimate.com. EL also recommends a simple safety standby gas treatment system
Eric Moore wrote:
I am trying to find out what would happen if the 4th line [at Onagawa nuclear plant] had also been damaged. Being just a member of the public I incorrectly thought that cold shut down rendered a plant safe. Am I right that electricity and working systems are needed to keep a plant safe (If so for how long before you do not need electricity.
While a few of the backup diesel power stations in NE Japan were shut down for maintenance, and some were leaking fuel, about three power plants in the region switched over to back-up power and did fine. There is also a spent fuel re-processing facility in Aomori Prefecture that faced station blackout and switched over to diesel power. It appears it took 3-9 hours to restore external power to these multiple locations. The Onagawa nuclear plant was not shut down as a precaution but because of a fire in a turbine as a result of March 11 quake (not a lot of details). Many of the power plants and spent fuel storage locations in Japan are now requiring mobile diesel generating trucks to be on hand for back-up power (government advised these purchases be made by end of April). Here is a status update from Kyodo on recent aftershocks:
Some water spilled out of the spent fuel pools at Onagawa as a consequence of the aftershocks. This is consistent with what happened to Kashiwazaki-Kariwa Nuclear Plants after 2007 Chuetsu earthquake (magnitude 6.6), and presumably at Fukushima (although some are still denying this). I suppose nobody wants to design covers or containment systems for these spent fuel pools, likely because it would be a massive retrofit, and also add even more vulnerable components and safety systems to deal with steam and hydrogen management and electricity backup to run fans, venting, filters, etc. A simple improvement, to my mind, would be to provide battery backup for standby gas treatment system (to vent gas from secondary containment and keep reactor building under negative pressure). As far as I know, the hydrogen gas treatment systems don’t have any separate battery or diesel backup (but relies on the same back up diesel generation that is supposed to run the entire cooling system at the time of a station blackout). Could such a simple secondary backup power source (of minimal voltage) have prevented the hydrogen explosions at 3 of the Fukushima plants?